The invention relates to digital communications systems and in particular is useful in carrier current transmission systems. In my copending application Ser. No. 307,705 filed Oct. 2, 1981 with Michael E. Wright and Robert S. Sleeth titled DIFFERENTIAL SAMPLE AND HOLD COUPLING CIRCUIT, and assigned to the assignee of the present invention, a digital carrier current receiver is described. A comparator provides the digital receiver output in a frequency modulated system which provides a degree of noise immunity. However, a carrier current system is still subject to the impulse noise commonly present on power lines and additional noise suppression is very desirable. The present invention relates to a time domain filter that can be incorporated into a carrier current receiver after the above-mentioned comparator.